1. Technical Field of the Invention
The invention relates generally to communication systems; and, more particularly, it relates to coding and modulation of signals within such communication systems.
2. Description of Related Art
Data communication systems have been under continual development for many years. In recent years, communication systems employing concatenated coding schemes of various types, like turbo coding, or LDPC (Low Density Parity Check) coding have attained significant interest. In combination with iterative decoding, these types of communication systems can achieve relatively low BERs (Bit Error Rates) near the Shannon limit of a given communication channel.
The Shannon limit may be viewed either as the lowest SNR (Signal-to-Noise Ratio) at which for a given data rate theoretically error-free data transmission may be accomplished, or the maximum data rate for error-free transmission over a channel with given SNR. The ideal goal has been to closely approach the Shannon limit with affordable complexity and limited latency for decoding and decoding while maintaining a given target BER performance.
LDPC coding has been shown to provide for excellent error performance near the Shannon limit in some cases. In one example, by using a so-called irregular LDPC code with a block length of one million bits performance within 0.1 dB of the Shannon limit for a BER of 10−6 has been shown. However, most applications require shorter block lengths leading to lower complexity and smaller latency for encoding and decoding. LDPC coding is considered as a premier candidate technology for such applications as well.
The use of LDPC coded signals continues to be explored within many newer application areas. For example, the use of LDPC coded modulation has been of significant concern within the IEEE (Institute of Electrical & Electronics Engineers) P802.3an (10GBASE-T) Task Force. This group has been chartered by IEEE with the development and standardization of a new Ethernet standard for 10 Gbit/s transmission over copper cabling with four twisted pairs and a cable length of up to 100 m. Public information concerning the IEEE P802.3an (10GBASE-T) Task Force is available at the Internet address http://www.ieee802.org/3/an/. Near-capacity achieving coded modulation is required to enable 10 Gbit/s operation over the envisaged copper cabling at a target BER of 10−12. An upper limit on latency of 2048 modulation intervals, or 25'600 bits on four wire pairs, precludes the use of most traditional concatenated coding schemes.
Clearly, there is a need in the art for a coding scheme which permits achieving the objectives of a project like IEEE P802.3an.